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In Arkansas cotton: Site-specific approach targets nematodes

Elton Robinson Farm Press Editorial Staff | Feb 17, 2006

In the late 1990s, Portland, Ark., cotton producer Bruce Bond had had enough of root-knot nematodes robbing his cotton yields. He decided to see what kind of response he could get from applications of the fumigant Telone.

The producer planted strips with and without Telone, applied with a modified ripper hipper. “We made 191 pounds more to the acre where we put the Telone compared to where we didn't. This wasn't a scientific analysis. We didn't replicate any of the plots. It was 16 rows with Telone and 16 rows without. But it really opened our eyes,” said Bond, a panel speaker at the Conservation Systems Cotton and Rice Conference, in Tunica.

Bond also realized that the fumigant (about $13 a gallon at 3 gallons per acre) was costly, “even though he was already doing a ripping and hipping operation. So in 2004, he ran an experiment on a site-specific application of Telone on 17 acres, with the help of Terry Kirkpatrick, a nematologist from the University of Arkansas.

“The question is whether or not it made sense to economically manage root-knot nematodes site specifically,” said Kirkpatrick, who was also on the panel. “The technology is there to put out anything we want, any way we want, including Telone or Temik.”

Kirkpatrick's studies have indicated that yield loss due to nematodes is directly related to soil type. His research on Bond's farm in 2002 indicated that if soil type was comprised of 60 percent sand, “you could make a 2-bale crop if you didn't have more than 150 nematodes in the soil sample. If you have 30 percent to 40 percent sand, you can have 2,100 nematodes and still make a 2-bale crop.

“So if a farmer asks me if he has too many nematodes, my question would be what is his soil type, and what's the percent of sand in that soil. If it's one type of soil, it may be way under. If it's another, it's too many and he needs to control it.”

In 2002, Kirkpatrick used a Veris mapping cart to map soil type on the 17-acre field. “Once you map this, the soil type is not going to change unless somebody levels the field. You can define places in the field that are sandier, clay or in-between.”

Kirkpatrick divided the field into four categories — 30 percent sand or less, 31 percent to 45 percent sand, 46 percent to 60 percent sand and above 60 percent sand. The researchers then looked at their nematode samples to determine where a specific application was necessary.

They used a low-tech approach to apply Telone to the field. “We had a map of the field in the cab of the tractor, which had a GPS,” Kirkpatrick said. “When we got to a point in the field where the soil texture and the number of nematodes dictated a threshold, we flipped on a switch to apply Telone, and when we got out of the spot, we switched it off.”

The researchers also ran strips where Telone was applied in blanket applications and a control strip where no nematicide was used at all.

“Where we use the 3-gallon, blanket rate of Telone, we bumped yield over the control by 133 pounds. Where we used the variable-rate, we bumped it by 75 pounds over the control, but we used 36 percent less Telone.”

The next year, Kirkpatrick expanded the test to northeast Arkansas, to a 162-acre field on the farm of Manila, Ark., cotton producer David Wildy. “We ran 10 test strips, a uniform application of Telone, site-specific Telone and no Telone. Sometimes the 3-gallon blanket rate of Telone was better, sometime the site-specific Telone was a little better.”

On average, the 3-gallon rate of Telone yielded 113 pounds higher than the check while the site-specific application yielded 93 pounds higher than the check along with a 42 percent reduction in Telone. The blanket rate of Telone resulted in $9,000 more in gross income across the 162-acre field when compared to the check plot. Costs included $30 for soil sampling and $6,400 for Telone. Net return was $2,600.

The site specific application resulted in $7,500 more in gross income over the check plot. Costs included sampling costs of $200 and Telone costs of $3,700. The net was $3,500.

“The question is whether the $1,000 you get from a site-specific application over a blanket application is worth your time and effort. It's easy to turn the application rig on when you enter the field and turn it off when you leave. But $1,000 across several fields will add up.”

The researchers have not studied a true variable-rate application of Telone. “We're not close to determining whether we can go with 1.5 gallons or 3 gallons of Telone,” Kirkpatrick said. “Right now, if it's a problem, we need to kill them. If it's not a problem, we need to leave them alone.”